Degree of Symmetry

Symmetry implies that several surfaces may share a common axis or centre line. It can also mean that a number of surfaces might share a common locating system. This being the case, symmetrical parts can usually be machined with fewer setups and in such a way that each setup can produce more than one machined surface. The resulting advantages are: increased accuracy, economy, and ease of handling, especially when the workpiece is made up from basic cylindrical shapes generated about the same center line, as in a turning operation.

Because the purpose of dimensioning on the part drawing is to relate surfaces, it becomes obvious that the dimensioning system itself is the best method of determining the number of surfaces that can be related in one setting of the workpiece. As in the case of the symmetrical part, related surfaces often share the same seat of registry.